Production of metals



miientecl Feb. 19, 1952 PRODUCTION OF METALS Charles H. Winter, J12, Wilmington, Del., assixnor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing.

Application December 24, 1948,

Serial No. 67,241

Claims. 1

This invention relates to the preparation of metals by reduction of their halides and through reaction with a metallic reducing agent. More particularly, it relates to novel methods for preparing pure titanium or zirconium by the reduction of the halides of such metals with a particular type of metallic reducing agent. I

Titanium and zirconium, due to their nonavailability in commerce, have been heretofore classed as "rare metals. This unavailability has been due to the diiiiculties encountered when attempts are made to separate these metals from the ores and compounds in which they exist. At present, these metals are of first rank importance, especially in view of theid potential uses in aviation and other fields.

The classical sodium reduction method for producing titanium originally involved the heating of titanium tetrachloride and metallic sodium in a steel bomb. In such process the sodium reacts with the chloride to produce sodium chloride and free elemental titanium, with consequent avoidance of the possibility of contamination of the titanium with oxygen. More recently, other metallic reducing agents have been suggested, including calcium, magnesium, aluminum, and potassium. In these latter proposals the reducing metal must be highly reactive and must not alloy appreciably with the desired metal product. Also, the recovered chloride by-product must be readil separated from the metal being produced. Magnesium has proven particularly useful and desirable for this purpose because it does not alloy with titanium and furthermore is readily available in large quantities. The reactions of zirconium halides with magnesium or the other reducing agents mentioned are somewhat analogous to those of titanium halides.

Several disadvantages attend these prior methods. The reduction operation, which generally is effected at temperatures rangin from 750-1100 0., produces a metal sponge which attaches itself to the internal walls of the reactor. tenaciously adheres thereto and eventually "grows across its upper or top portion. Removal of this sponge from the reactor can be efiected only by expensive, tedious, and timeconsuming chipping, reaming Or other forciblydetaching operations. The highl corrosive nacult. The metal sponge must be purified and melted prior to use. In the finishing treatments to which it is subjected. sponge density is a most important consideration. Due to the continuous variance of the level of the reactants in the reaction vessel in accordance with reducing metal consumption and combination with the halogen present to form the halide salt, considerable variance in sponge density also takes place. Hence, the density of the final product varies with the volume of growth experienced by the metal sponge. A real need thus exists for an improved process wherein an effective control may be be readily obtained without the disadvanta es ture of the titanium or zirconium halides used is also disadvantageous and subjects the metal or other materials present in the equipment used to constant, undesired attack. Control over the quality of the metal being produced is also dlflireierred to. A special object is to provide a novel method and means for retaining the reaction or reducing metal within a removable, confining structure or frame within a suitable reaction zone and in which the sponge metal reaction product forms out of contact with the internal surfaces of said zone to be subsequently removed therewith from said zone for recovery and puriflcation treatment. An additional object is to eflect removal from and recovery of said metal sponge product without any attendant damage to or interference with the continued operation of the reactor or reaction zone. Other objects and advantages will be evident from the ensuing description.

These objects are attained in my invention for obtaining a pure metal substance which comprises floating a metallic reducing agent upon a bath of an inert, molten metal halide salt in a retaining element within and out of contact with the internal surfaces of a reaction zone, reacting said reducing agent with a metal halide reactant in said zone at an elevated temperature, under an inert atmosphere, upon completion of the desired reaction, removing said retaining element from said zone together with the metal reaction product which forms therein and adheres thereto, removing the metal reaction product from said retaining element and subjecting said product to purification treatment.

tallic reducing agent sufiicient to effect a partial filling of said vessel, submerging the partially-filled vessel in an inert, molten halide salt bath within a reaction zone and to such a depth in the bath as will float the reducing metal in said retaining vessel and elevate its level to substantially the upper extremity or rim of that vessel, thereafter maintaining the reaction zone at a temperature ranging from '750-ll00 C. under an inert gaseous atmosphere. introducing a halide of said titanium or zirconium metal into said reaction zone onto the surface of the floating reducing metal, upon depletion of the reducing metal removing the retaining vessel together with its adhering metal sponge reaction product from said 'zon'e, removing said reaction product from said vessel and subjecting said product to purification treatment.

In one specific embodiment of the invention, involving preparation of pure titanium metal, a

molten metallic reducing agent, such as mag nesium or calcium (or other metal havinga reducing potential greater v than titanium) is charged into an open-ended steel or other suit able type of metallic retaining vessel having supporting side walls and a cool, discontinuous, or apertured base portion. One particularly useful form of vessel for this purpose comprises a receptacle shaped in the form of a common flower pot provided with a base having one or more small openings or vents adapted to allow free and open communication between its interior and ametal salt bath in which the receptacle is to be submerged for a purpose and in a manner to presently appear. The charging of the molten metal continues until a required proportion of such metal becomes introduced and a partial filling of said vessel therewith is efl'ected. Due to the cooling effect which contact of the molten metal with the cool surfaces of the base portion induces, part of the molten metal "freezes or solidifies to temporarily seal oil or close the communicating vents in said base and cause retention of its molten metal content within the retaining vessel; The partially-filled receptacle is then partially submerged to near its upper rim or edge portion in an inert, molten metal halide salt bath (preferably magnesium chloride) within a suitable reactor or reaction zone. The heat content of the salt bath remelts the solidified reducing metal within the apertured base to permit flowing of the molten liquid halide or chloride bath into the interior of the retaining vessel to force its reducing metal (magnesium or calcium) content to float upwardly therein and to within a relatively short distance from the top or upper extremity thereof. The reactor is then closed and the whole is then heated to a temperature not exceeding the boiling point of the reducing metal and to, say, about 800-950 C. under an atmosphere of an inert gas, preferably argon. Upon the reactants becoming satisfactorily molten, liquid titanium tetrachloride is conveniently introduced at a controlled rate into the reactor and onto the surfaces of the floating metallic reducing agent. It thereupon becomes immediately vaporized by the contained heat of the reactor and reacts with the reducing metal, forming the desired titanium metal sponge. Its released halo en 20 apertured base of the latter.

4 forms the corresponding halide salt of the reducing metal which sinks to the bottom of the reactor to join the supporting bath. The titanium sponge reaction product forms at the top or lip s portion of the retaining vessel, grows outwardly'and upwardly therefrom, but, due to the spaced relationship of'said vessel from the internal walls of the reactor, remains out of contact with such internalwalls. The degree to which the retaining vessel is submerged in the salt bath varies in accordance with the level of said bath and hence assures at all times the existence of constant conditions within the reactor throughout the reaction. when the desired reaction is completed,

further heating is discontinued. The retaining vessel is then raised above the level of the salt bath to permit drainage from it and the titanium sponge of any metal halide salt, such drainage being discharged from the vessel through the The retaining vessel, with its contained metal sponge reaction product, is then conventionally cooled within, or externally of the reactor in an inert atmosphere. After the desired cooling, the metal sponge reaction product can be recovered from the vessel through suitable boring on a lathe or by manual or other means, such as by chipping or chiseling it away to effect removal and recovery. The resulting chips may then be subjected to water or other type of washing treatment to remove magnesium halide therefrom, or may be subjected to suitable vacuum treatment to bring about the desired purification. Conventional purifying treatments of this type comprise those disclosed in U. S. Patent 2,205,854. Following its purification,

as the follwing specific examples are given, which are merely illustrative of and not to be construed as limiting the underlying scope of the invention:

Example I Into a rectan ular steel retaining vessel, 8" in height, having horizontal dimensions of 12" by 48" at the top, tapering to 10" by 46" at the base, and in the bottom of which 3 evenly-spaced vents, each of 2" diameter, are provided, 120 lbs.

of molten liquid magnesium metal were charged to fill the vessel to a depth of 4". The base of this vessel or pot was set on a cold block to freeze partially the liquid magnesium and prevent its exit therefrom through the holes or vents. This the vessel was about 1 above the level of said bath. The heat content of the magnesium chloride caused the solidified magnesium metal to remelt and allow a portion of the liquid chloride to enter said vessel through the vents to force the magnesium present therein to float upwardly to within of its top or rim portion. The whole mass was then enclosed in the reactor and heated to a temperature of 850 C.. in an atmosphere of argon. Liquid titanium tetrachloride was then introduced into the argon atmosphere and onto the surface of the floated magnesium at the rate of about 100 lbs. per hour, the combined TiCl4-argon pressure being slightly greater than 1 atmosphere, or approximately 765 mm. Hg. The TiC'h liquid was immediately atmosphere.

l vaporized by the contained heat o! the reactor and reacted with the Mg melt to produce MgCl: (which immediately descended to join the MgCl: bath) and the desired Ti metal sponge. The latter formed at and was retained on the rim of the retaining vessel. When essentially all of the reducing metal had been consumed, said vessel together with its adhering metal sponge reaction product was raised from the bath to permit any MgCh to drain from the sponge via its vents, and the whole then cooled conventionally in the inert The Ti sponge, filling the top of the retaining vessel and above it, had an average thickness of 4". comprise 100 lbs. Ti: lbs. Mg; 40 lbs. MgClz, together with traces of TiCla and TiClz. Upon being purified by conventional vacuum distillation treatment the final, desired pure Ti metal wasrecovered.

Example II Upon analysis, it was found to Example I was duplicated, except that stoichiometric proportions of magnesium and zirconium chloride were subjected to reaction with a temperature of 825 C. prevailing in the reactor. As in the above example, a highly satisfactory metal product consisting. of pure zirconium was recovered.

While described as applied to certain specific and preferred embodiments, the invention is not, as indicated, restricted thereto. In general, use is contemplated of any reducing metal which is more electropositive than the titanium or zirconium to be produced. Metals especially useful include those which in aqueous solutions would have electrode potential values of 1.70 or greater, as shown by the electromotive force series. Of these, the alkali and alkaline earth metals are particularly adaptable since their electrode potentials are all greater than 2.0, a fact which insures rapid reaction at the 750 C. or higher temperature which is usually employed in the process. Specific examples of reducing metals contemplated as useful include magnesium, calcium, barium, strontium, aluminum, sodium, potassium or lithium. These metals are molten at 750 C. or higher and have relatively low specific gravities which permit them to be floated on the most suitable metal halide salt baths. Of the group mentioned, calcium and magnesium are preferred for use. although magnesium is most preferred because of its high potential and production of a residue in the reaction which is easily separated from the metal being produced.

A variety of halide salts may be employed as the molten metal bath, provided such salts are substantially inert with respect to the reactants. There are, however, certain restrictions as to the combinations of supporting bath and reducing metal which may be employed herein. The relative densities of reducing agent and supporting salts and the pressures maintained within the reaction vessel are the most critical factors. The metal must be less dense than the support: and both must be liquid within the same temperature and pressure range. Preferably, use is made of a bath salt which is the same salt as that being produced in the reaction. For example, when TiCh is being reduced by magnesium, the magnesium may be floated on a melt of magnesium chloride; and when calcium or other alkaline earth metals are employed as the reducing agent, a melt of the corresponding alkaline earth metal halide, especially chloride, is preferably employed as the bath salt. Similarly. sodium may be supported on sodium chloride.

when the sodium reduction method is resorted to; potassium on potassium chloride. and calcium on calcium chloride, etc. Alternatively, magnesium may be floated on its bromide salt and sodium or potassium on their respective bromide or iodide salts, etc. Neither magnesium nor sodium, however, may be used with their fluorides with atmospheric pressure, due to the fact that the fluorides are solid at a temperature where the metals volatilize. However, such systems can be resorted to with addition of a lower melting halide salt, such as sodium or potassium chlorides. Oxygen-containing compounds are not desirable for use in the invention, due to the reactivity of titanium or zirconium therewith and the consequent contamination of the metal product being produced. Except for these obvious restrictions of density and melting temperatures, it will be understood that in general any combination of reducing agent and molten liquid metal halide support may be employed in the invention.

The two metals which this invention is particularly useful for producing comprise titanium and zirconium. In their production any of the halides of these metals may be employed, especially those in which the halogen component has an atomic number greater than 9, i. e., chlorine, bromine, or iodine. The chlorides, such as TiCh and ZrCh, are especially useful and are the most economical, practical and readily obtainable. While chlorides are preferred, the bromides, iodides or fluorides of these metals are contemplated for use, as already indicated. The fluorides are all solid and hence are not susceptible to ready introduction into the reactor. The alkaline earth fluorides resulting therefrom are insoluble in water and hence difficult to eliminate in the subsequent purification operation. Iodides and bromides are also solid at room temperature and, though employable, are economically disadvantageous due to their relatively high cost.

The only major difference between the titanium and zirconium-producing processes is that when using the tetra-chlorides at atmospheric pressures zirconium tetrachloride is a solid which sublimes at about 300 C., while titanium tetrachloride is a liquid between -30 C. and 136.4: C. Thus, the chosen method of addition of zirconium tetrachloride may be different. Aside from this, the involved halides may be added in any desired form, either as solids, liquids, or vapors. If added as liquids, or as solids, they become volatilized upon introduction into the heated reaction vessel.

While the use of argon has been mentioned as a preferred type of protective or inert gas in the invention, other inert gaseous elements of the group zero of the periodic system, such as helium or neon, as well as mixtures thereof, can be employed, as can any other protective and inert gas which is free from undesirable reactants, especially oxygen and nitrogen.

One most important feature of this invention is the provision and use of the special retaining element or frame member within a con-v ventional reactor employed for producing metals by reduction of their halides. It is obvious that structure other than that described and which is provided with supporting side walls adapted to confine the reducing metal therein and prevent its horizontal intermingling with the bath salts as well as with a base portion which is in open communication with the salt bath to allow free vertical flow of the liquid content of the reactor spears can be readily utilized. The structure so employed may comprise one without such base portion or may comprise a vessel shaped in any desired form or of any dimension in which one or more vents or apertures are, provided in its lower extremity. The vents present may be of the same or differing sizes and shapes, and if desired need not exist in said base portion, but may be present in the lower extremity of said side walls and below the level at which the reducing metal is to be floated, or may be in both side walls and base portion.

The positioning or partial submergence of the vertical retaining element in the bath of molten halide salt and within the reactor itself is also an important consideration. As already noted. its external, confining walls are preferably disposed in spaced relationship from the internal walls of the reactor to thereby prevent formation or deposition of the metal reaction product upon such latter walls. During reaction, the surface of the molten metal bath is maintained below and short of being flush with the outer rim of suchelement, while the floating reducing metal confined in the latter is elevated to a point immediately below the internal upper rim of that element, due to the upward flow of the molten salt bath through its base. Control of this degree of submergence may be achieved through suitable mechanical. means or by adjusting the relative areas of reactor and bath surfaces. This will effectivelystandardize the density of the final sponge metal product. If desired, the retaining element may be first submerged to its desired depth in the salt bath and the reducing metal can be then introduced into it in either molten or solid state. The positioning and use of such retaining structure within the reactor effectively protects the internal surfaces of the latter from undesired severe corrosion which the presence and use of titanium or zirconium halides would otherwise normally induce. Also, it enables ready withdrawal from the reactor of the metal sponge reaction product without the dificult, expensive and time-consuming operations of prior methods.

,Of considerable practical convenience also is the self-tapping and ready draining of molten byproducts through the discontinuous base which the employment of the retaining structure of this invention affords. Finally, the use of such structure renders possible a mechanized or semicontinuous method for producing pure titanium or zirconium metal in lieu of the slow, tedious and batch procedures of the prior art.

In one useful. alternative embodiment of the invention, the steps of the present process may be conveniently mechanized to provide a continuone type of operation. Thus. the retaining vessel, suitably charged with the desired amount of metallic reducing agent, may be placed on a track means and drawn, in an enclosed tunnel or confining space, through a bath of an inert, molten-metal halide salt, passing first through a preheating zone where the reducing metal becomes melted; thence through a reaction zone maintained at the desired elevated temperature. and under an inert gaseous atmosphere, where the titanium or zirconium halide is conveniently introduced and reduced; and finally through a cooling zone, also maintained under an inert atmosphere, where the track emerges completely from the bath to allow the halide salt to drain from the resulting metal sponge product. The

height of the track in the reaction zone may be varied as desired to control the degree of sub- Example III A series of steel retaining vessels similar to that employed in Example I was set up, each being suitably coupled to the next. As in Example I, each was charged. about halt full with magnesium metal and then lowered down a vertical shaft. provided with locks and an argon atmosphere. into a horizontal tunnel. nel was equipped with rails along which each vessel was drawn and at a speed of 25 feetper hr.. with each vessel being 12 min. apart. The first ft. of the tunnel contained molten MgClz, to provide the, conditions of Example I. that-is, preheating and reaction zones. TiCh was added at about the center of this distance, at the rate of 2000 lbs. per hr., to react as usual with the heated and melted magnesium and form titanium sponge at the rim of each pot. The MgCl-z level was kept constant by means of an overflow system, and excess MgClz was discharged therethrough at '1800 lbs. per hr.

At the end of this 100-foot zone. the rails sloped upward sharply out oi the bath, so that excess MgClz drained from the retaining vessels through their vents. Each vessel was then cooled'gradually and successively in a 75-foot extension of the same tunnel and emerged through conventional gas locks at the exit end. to become ready for recovery and purification of the Ti sponge adhering thereto in accordance with said Example I. This sponge was similar in composition to that of Example I.

Under the above conditions, each retaining vessel traveled a tunnel ft. in overall length in 7 hrs., and the hourly production rate of titaniibim, when in full operation, approximated 500 I claim as my invention:

1. A process for producing a metal selected fromthe group consisting of titanium and zirconium through reduction within a closed reaction vessel of a halide of said metal the halogen component of which has an atomic number 7 greater than 9, comprising floating in said vessel out of contact with its internal walls and upon an inert molten reducing metal halide salt bath maintained therein a reducing metal more electropositive than the metal under production. confining the floated metal within an open receptacle therefor which is partially immersed in said .salt bath with. its base and interior portions being maintained in open communication with said bath. reacting said reducing metal with said metal halide reactant at an elevated temperature, subsequent to said reaction removing said receptacle and the resulting metal reaction product which it contains from said bath and the reaction vessel, and purifying said metal reaction product thus obtained.

2. A process for producing a metal selected from the group consisting of titanium and zirconium through reduction within a closed reac- This tuntion vessel of a halide of said metal the halogen component of which has an atomic number greater than 9, comprising floating in said vessel out of contact with its internal walls and upon a inert molten metal halide salt bath of the reducing metal employed in the process of reducing metal more electropositive than the metal under production, confining the floated metal within an open receptacle therefor which is partially immersed in said bath with its base and interior portions maintained in open communication with said bath, reacting said reducing metal with said metal halide reactant and at temperatures ranging from 750-1100 C. in an atmosphere of an inert gas, subsequent to the reduction reaction raising said receptacle togetherwith its contained metal reaction product above the level of said molten metal halide salt bath, allowing the raised mass to cool under an inert atmosphere, thereafter removing said receptacle and metal reaction product from the reaction vessel and purifying said product after its separation from said receptacle.

3. A method for producing titanium metal through reduction in a closed reaction vessel of titanium tetrachloride with magnesium which comprises floating the magnesium upon a bath of molten magnesium chloride which is maintained in said vessel and within an open. confining receptacle therefor which is partially immersed in said bath with its base and interior portions being maintained in free and open communication with said bath, reacting the magnesium with the titanium tetrachloride and at temperatures ranging from about 850-950 C. in an atomsphere of an inert gas, upon depletion of themagnesium reactant lifting the receptacle together with its adhering metal reactant product above the level of the magnesium chloride bath within said vessel to allow magnesium chloride to drain therefrom, cooling the thus-raised mass under an inert atmosphere within said vessel, thereafter removing the receptacle and cooled titanium metal product from the reaction vessel, separating said product from said receptacle and subjecting it to purification treatment.

4. A process for producing titanium metal which comprises floating calcium metal within an open confining receptacle therefor and upon a bath of molten calcium chloride maintained in a closed reaction vessel and in which bath said receptacle is partially immersed with its base and interior portions maintained in open communication therewith, reacting said; calcium metal with titanium tetrachloride at temperatures ranging from 850-950 C. and under an atmosphere of an inert gas, upon depletion of the calcium reactant raising said receptacle together with its contained titanium metal reaction product above the level of the calcium chloride bath, allowing the raised mass to cool and drain under an inert atmosphere, removing the receptacle and its titanium metal product from the reaction vessel, separating said product from said receptacle, and subjecting the product to purification treatment.

5. A process for producing titanium metal which comprises-floating sodium metal within an open, confining receptacle therefor and upon a bath of molten sodium chloride maintained in a closed reaction vessel and in which bath said receptacle is partially immersed with its base and interior portions in open communication therewith, reactingthe sodium metal with titanium tetrachloride and at temperatures ranging from 850-950 C. under an atmosphere of an inert gas, upon depletion of the sodium reactant raising said receptacle together with its contained titanium metal reaction product above the level of the sodium chloride bath, allowing the raised mass to cool and drain under said inert atmosphere, removing the titanium metal product and receptaclefrom the reaction vessel, separating said product from said receptacle and subjecting it to purification treatment.

CHARLES H. WINTER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. A PROCESS FOR PRODUCING A METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM THROUGH REDUCTION WITHIN A CLOSED REACTION VESSEL OF A HALIDE OF SAID METAL THE HALOGEN COMPONENT OF WHICH HAS AN ATOMIC NUMBER GREATER THAN 9, COMPRISING FLOATING IN SAID VESSEL OUT OF CONTACT WITH ITS INTERNAL WALLS AND UPON AN INERT MOLTEN REDUCING METAL HALIDE SALT BATH MAINTAINED THERIN A REDUCING METAL MORE ELECTROPOSITIVE THAN THE METAL UNDER PRODUCTION, CONFINING THE FLOATED METAL WITHIN AN OPEN RECEPTACLE THEREFOR WHICH IS PARTIALLY IMMERSED IN SAID SALT BATH WITH ITS BASE AND INTERIOR PORTIONS BEING MAINTAINED IN OPEN COMMUNICATION WITH SAID BATH, REACTING SAID REDUCING METAL WITH SAID METAL HALIDE REACTANT AT AN ELEVATED TEMPERATURE, SUBSEQUENT TO SAID REACTION REMOVING SAID RECEPTACLE AND THE RESULTING METAL REACTION PRODUCT WHICH IT CONTAINS FROM SAID BATH AND THE REACTION VESSEL, AND PURIFYING SAID METAL REACTION PRODUCT THUS OBTAINED. 